1. Field of the Invention
The present invention relates to a display driving apparatus, and particularly to a display driving apparatus having a variable driving ability.
2. Related Art
FIG. 1 shows a general configuration of the conventional liquid crystal driving apparatus. As shown in FIG. 1, the conventional liquid crystal driving apparatus has a liquid crystal display 11, a source driver 12 made up of several drive units 121 to 12n, each driving corresponding source electrodes in the liquid crystal display 11, and a gate driver 13 made up of several drive units 131 to 13n, each driving units 131 to 13n driving gate electrodes in the liquid crystal display 11.
When a drive current is applied to the liquid crystal display 11 from one of the drive units 121 to 12n, while also applying a drive voltage from one of the drive units 131 to 13n, a corresponding pixel on the intersection of the applied drive current and the applied drive voltage will be activated.
FIG. 2 shows an equivalent circuit to the liquid crystal display 11, as an example. As shown in FIG. 2, the equivalent circuit is comprised of resistors R and capacitors C. Note that inductors (not shown) are also included in the liquid crystal display 11 in FIG. 2. A row of the liquid crystal display 11 is driven by a amplifier 14 prepared in the end of a source driver 12.
However, in the structure described earlier there are the following problems: the larger the liquid crystal display 11 becomes, the heavier its load becomes. In addition, the load of the liquid crystal display 11 may be uneven due to an error in its manufacturing process. A ringing noise may occur on the line of the liquid crystal display due to the negative characteristic of the amplifier 14 (e.g., caused by the feed back loop in the amplifier""s structure) and the structure of the equivalent circuit shown in FIG. 2. This potential ringing noise cannot be prevented as long as the driving performance of the amplifier 14 is fixed and not flexibly changed in accordance with its error. Furthermore, when the liquid crystal display has a low amount of load to the drive performance of the amplifier 14, overshoot and undershoot noises may appear on the line driven by the amplifier 14. The ringing, overshoot, and undershoot noises cause an image degradation on the liquid crystal display.
Accordingly, an objection of the present invention is to provide a display driving apparatus and a display system which will effectively prevent the image degradation from occurring.
According to an aspect of the present invention, a display driving apparatus is provided, comprising: variable-resistor means through which a current is supplied for a data line of a display; and a selection means for selecting a resistance of the variable-resistor means. As an example, the variable-resistor means can be realized using analog switches S1 and S2 shown in FIG. 3, while the selection means can be realized by a selection circuit shown in the same.
According to another aspect of the present invention, the display driving apparatus further comprises current changing means for changing the aforementioned current. The current changing means can be realized with the combination of circuits 21 to 24, and a bias circuit 3 shown in FIG. 3.
According to yet another aspect of the present invention, a display system is provided, comprising: display means, comprised of a plurality of scanning lines and data lines, and a plurality of pixel cells(transistors) placed on the intersections of the plurality of scanning lines and the plurality of data lines, for displaying an image; data line driving means comprised of a plurality of source drivers, each driving each corresponding data line in the display means, wherein each source driver comprises variable-resistor means through which a current is supplied for each data line in the display means, and a selection means selecting a resistance of the variable-resistor means; and scanning line driving means for driving each scanning line in the display means. An exemplary structure of the display system is shown in FIG. 9. In this exemplary structure the display means corresponds to a display panel 1100; the data line driving means corresponds to the combination of a source driver 1200 and a port-A 1700; and the scanning line driving means corresponds to the combination of a gate driver 1300, an AND gate 1500, and a port-B 1600.